A mobile ad hoc cognitive radio network is an ad hoc network implementing cognitive radio technology.
Ad hoc networks are self-forming networks which can operate in the absence of any fixed infrastructure, and in some cases the ad hoc network is formed entirely of mobile nodes. An ad hoc network typically includes a number of geographically-distributed, potentially mobile units, sometimes referred to as “nodes,” which are wirelessly connected to each other by one or more links (e.g., radio frequency communication channels). The nodes can communicate with each other over a wireless media without the support of an infrastructure-based or wired network. Links or connections between these nodes can change dynamically in an arbitrary manner as existing nodes move within the ad hoc network, as new nodes join or enter the ad hoc network, or as existing nodes leave or exit the ad hoc network. Because the topology of an ad hoc network can change significantly techniques are needed which can allow the ad hoc network to dynamically adjust to these changes. Due to the lack of a central controller, many network-controlling functions can be distributed among the nodes such that the nodes can self-organize and reconfigure in response to topology changes.
One characteristic of ad hoc network nodes is that each node can directly communicate over a short range with nodes which are a single “hop” away. Such nodes are sometimes referred to as “neighbor nodes.” When a node transmits packets to a destination node and the nodes are separated by more than one hop (e.g., the distance between two nodes exceeds the radio transmission range of the nodes, or a physical barrier is present between the nodes), the packets can be relayed via intermediate nodes (“multi-hopping”) until the packets reach the destination node. In such situations, each intermediate node routes the packets (e.g., data and control information) to the next node along the route, until the packets reach their final destination. For relaying packets to the next node, each node maintains routing information collected through conversation with its neighboring nodes. The routing information can also be periodically broadcast in the network to reflect the current network topology. Alternatively, to reduce the amount of information transmitted for maintaining accurate routing information, the network nodes may exchange routing information only when it is needed.
Cognitive radio technology includes the capability of mobile nodes to alter transmission parameters based on knowledge of its environment. For example, a cognitive radio network can be a network of mobile communication nodes (hereinafter referred as nodes) in which a mobile communication node changes its transmission or reception parameters to communicate efficiently in order to avoid interference with incumbent users. This alteration of parameters is based on active monitoring of several factors in the external and internal radio environment, such as radio frequency spectrum, user behavior and network state.
The nodes typically need to keep sensing the network so as to monitor presence of any high priority spectrum occupant to assure unimpeded spectrum access to the high priority spectrum occupant. Further, the nodes may need to keep sensing the network to make sure that quality of service on the network is not degraded. The network may choose to abandon a spectrum if it is sensed that the quality of network is degraded, such as, an unfavorable change in noise/interference floor, allowed transmit power, or propagation conditions (if either the network or the environment are in motion), or identification of another channel that offers increased or more reliable throughput.
There are several existing methods to save power in a mobile node. One such method provides for some nodes to go to sleep when there is a particular quantity of nodes in the network. Each active node makes measurement and transmits them. A node sleeps for a random amount of time. When the node wakes up, it checks a node report buffer. If the node report buffer is empty, the node immediately goes back to sleep. If the node report buffer has content, the radio of the node wakes up transceiver of the node and tries to transmit the measurements. Here, adaptive sleeping probabilities are calculated depending on whether nodes are dying off. Also, old measurements are pushed out of the node report buffer and not transmitted.
In another method for saving power in a mobile node a single repository for node powering status (battery or line powered) and Dynamic Frequency Selection (DFS) measurements is provided. DFS measurements are altered based on node power supply condition. Here, if some battery powered nodes are excluded from making measurements, then the nodes with reserve power are assigned more measurements. A node determines the duration of its sleep cycle based on its power status.
In the existing systems, nodes sense and transmit results regardless of the change from previous sensor results. This results in inappropriate utilization of communication resources.
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